For interferometric measurement or surveillance of samples, optical short-coherence tomography (also called OCT) is known. This principle allows optical sectioning cuts in the material in a highly sensitive manner, achieving axial resolutions, i.e. resolutions along the optical axis of incidence of the radiation, of few micrometers. The principle is based on optical interferometry and uses a partially coherent light source for resolution in depth direction, i.e. along the optical axes.
A known application for optical coherence tomography is that of measuring the eye, in particular the human eye. Carl Zeiss Meditec AG distributes a device for this purpose, which is called IOL Master and determines, inter alia, the eye length, i.e. the distance between the corneal vertex and the fundus. In doing so, the path length of the reference beam is modified during measurement. The device is applied, in particular, in connection with cataract surgery. In cataract surgery and refractive ophthalmic surgery, the refractive power of an intraocular lens to be implanted is determined on the basis of the pre-operative refractive condition of the eye, of the acoustically or optically determined length of the eye and of an estimation of the post-operative anterior chamber depth. Thus, precise knowledge of these parameters is required prior to the operation. The scanning process of the IOL Master provides a signal at the interferometer output, and the lengths to be measured are determined from the time course of the signal. This scanning process takes time; movements of the subject during measurement lead to errors or inaccurate results.
Further, a Fourier analysis interference method is known. For spatial resolution in depth direction, a spectrum of the interference pattern between the reference beam and the measurement beam scattered back from the sample is recorded. Recording can be effected simultaneously, using a spectrometer (for a suitable broadband light source), or sequentially (for spectrally sweepable sources). The inverted Fourier transform of the spectrum enables reconstruction of the structure along the depth direction.